User blog:Samuli.seppanen/Not so total rebuild?
I started the work on new ballista the previous weekend at the forge, focusing on the little arch and the little ladder, which were too wide. Instead of just shortening the little arch I decided to make the curved part shallower to increase its strength, because I suspected it might have been crushed a little. However, doing that while keeping the straight parts correctly aligned proved to very difficult. So I had to let go of the old little arch completely and start planning on making an entirely new one from fresh, round stock. Forging the shape first and then flattening is something I've done plenty and which works very well. On the bright side I did manage to forge nice U-shaped forks with sharp, 90 degree corners for the little arch with no difficulty. I also worked on a replacement little ladder beams, which I had finished earlier, but which were too long. Its tenons were formed by simply flattening the end of the beam carefully. This flattening technique seemed to work, but produced tenons that were somewhat narrower than what could be achieved by folding the beams into tenons. Anyways, after spending to much time in LibreCAD I had figured that separate tenons attached to the outer surfaces of the beams would make complying to the measurements in the cheiroballistra manuscript fairly trivial. So, armed with this knowledge, I cut of the tenons from the new beams and started forging separate tenons which would then be riveted to the beams. When forging the tenons I realized that the "rivet to the beams" part would be a fairly time consuming process. First I needed to flatten the inner part of tenons so that rivet holes would not make them overly weak. The rivets themselves could not be very thing, or they would give in. The outer ends also needed to be flattened along the other axis, so that adding the notch for the field-frame bar would be possible. While this was all possible, it was very time-consuming because the tenons would have to be straight and aligned correctly to rest tightly against the beams. So, in retrospect, the separate tenons seem too much trouble to be worth it: it's just so much easier to just forge the beams and the tenons from a single piece of steel. The next time I visit the forge I will remake the beams, probably from 6mm steel "just in case" and fold the beams into tenons or use the "flatten the beam into a tenon" technique with small modifications to produce a wider tenon. I've also started to question whether there is really need to remake the field frames, and possibly washers along with them. While the 320hz pretensioning did start bending the straight field-frame bar slightly (<1mm) outwards, that's nowhere near critical. Also, in Baatz (1978) it is told that the Gornea field frames have about 7mm thick bars, and that the rings are about 4mm thick. Of course the Gornea field frames have corroded quite a bit and the frame is squatter, but still 10mm for a much lighter weapon (=cheiroballistra) seems excessive. So I will give 350hz a spin using the current field-frames before I throw in the towel. If all goes well, I will probably save a full week's worth of effort. The "downside" of this approach will be that I will have to adapt the new little ladder and little arch to the old field-frames, which are slightly narrower than what I had planned for the next iteration. Category:Blog posts Category:Backup Category:Field frame Category:Little arch Category:Little ladder Category:Practical